1. Field of the Invention
The present invention relates to a cathode ray tube (CRT) monitor, and more particularly, to a processor for controlling the horizontal size of a monitor screen and a system thereof.
2. Discussion of Related Art
The horizontal size of a screen of a CRT monitor is generally controlled by a direct current (DC) voltage of a horizontal calibration signal. In particular, the optimum horizontal size of the screen is determined at different DC voltages according to video modes of the monitor.
A conventional method for controlling the horizontal size of the monitor screen uses the DC voltage of the horizontal calibration signal, which is used for calibrating the geometry at left and right sides of the screen. In other words, an alternating current (AC) element of the horizontal calibration signal is used for calibrating the geometry of the screen, while the DC element of the horizontal calibration signal is used for controlling the horizontal size of the screen.
FIG. 1 illustrates a horizontal calibration signal. The horizontal calibration signal, having a parabolic shape, is for compensating a phenomenon in which an image on a screen is distorted by the magnetic field of the earth that bends the electron beam of a CRT. The AC element of the horizontal calibration signal (EWVAC) is used for calibrating the geometry of the screen, and the DC element of the horizontal calibration signal (EWVDC) is used for determining the horizontal size of the screen.
FIG. 2 is a block diagram illustrating a conventional system for controlling the horizontal size of the monitor screen. The conventional system for controlling the horizontal size of the monitor screen comprises a microcomputer 210, a processor 220, and a driving circuit 230. The processor 220 includes two converters 240 and 250, respectively. The converter 240 generates an AC control signal ACTRLS, while the other converter 250 generates a DC control signal DCTRLS. The control signals CTRLS generated from the microcomputer 210 control the amount of current of the AC and DC control signals ACTRLS and DCTRLS. In this case, a pulse width modulation (PWM) port (not shown) is allotted to the microcomputer 210, so that the PWM port generates a first calibration signal PWS for controlling the horizontal size of the screen.
A calibration signal generation circuit 260 in the processor 220 receives the DC and AC control signals DCTRLS and ACTRLS for generating a second calibration signal EWCRS. By summing up the first and second calibration signals PWS and EWCRS, a third calibration signal SUMS is formed, and the driving circuit 230 generates the horizontal calibration signal EWOUT in response to the third calibration signal SUMS.
When only one converter 250 is arranged in the processor 220 for controlling the horizontal size, the horizontal size of the monitor screen is generally controlled by additionally using the PWM port of the microcomputer 210. In other words, by arranging a plurality of components for controlling the horizontal size of the monitor screen, the converter 250 in the processor 220 is used for controlling the horizontal size, typically while the monitor is being manufactured in a factory. The PWM port of the microcomputer 210 is typically used by the user for controlling the horizontal size. If noise is present in the first calibration signal PWS generated from the PWM port of the microcomputer 210, the noise can propagate and affects the horizontal calibration signal EWOUT.